1. Field of the Invention
This invention relates generally to an actuator such as an electric jack for adjusting the relative positions of adjacent structures.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Electro-mechanical actuators are used in a wide variety of commercial and industrial applications. Because they generally comprise simple linear actuators, such actuator systems can be integrated into mechanical systems for use in aligning or moving structures into desired positions relative to other structures or to applied forces or accelerations. One well known application of electro-mechanical actuator technology is the use of jack-type actuators to control the attitude or tilt of a rigid or semi-rigid platform, such as a recreational vehicle, relative to earth's gravity.
Position sensing systems, such as optical encoders and Hall Effect sensors are also known to be useful in many commercial and industrial applications. As shown in FIG. 4, a typical optical encoder includes a rigid, opaque encoder ring that may be supported on a shaft or other structure whose rotation is to be monitored. The encoder ring has angularly-spaced holes or slots that allow light to pass through. With a light source, such as an LED photo emitter, positioned on one side of the encoder ring, and a light detector, such as a phototransistor photo detector, positioned on the other side, a detection circuit connected to and receiving signals from the photo detector can sense whenever encoder ring rotation causes a hole/slot pass between the photo emitter and the photo detector. Because the holes/slots are spaced at regular angular intervals, rotation of the encoder ring will cause the photo detector to sense a continuous series of light pulses or pulse train as the shaft is spinning. By counting the pulses in a pulse train, the detection circuit can directly track the rotation of the encoder ring and shaft and can infer the motion of other connected structures. Additionally; the frequency/period of the pulse train can be used to calculate shaft rotational speed.
As shown in FIG. 3, Hall Effect sensors are typically mounted in fixed locations circumferentially spaced from one another and radially equidistant from a rotor magnet in positions allowing them to track rotor magnet rotation by sensing the passage of magnetic poles of the rotor magnet. Alternatively, a single Hall Effect sensor may be mounted adjacent the circular path of an array of magnets circumferentially spaced around and supported on a rotatable disk or wheel. According to this arrangement the stationary Hall Effect sensor tracks disk rotation by sensing the passage of the magnets.
When a position sensor such as an optical encoder or Hall Effect sensor is employed, the position of a rotating structure such as a wheel or shaft can be accurately ascertained, and the position of a connected structure inferred, by counting pulses in the direction of rotation. As shown in action step 1 in the logic diagram of FIG. 5, a controller's perception of an initial starting position or “home” position of the rotating structure is defined by the pulse count of a software pulse counter when the rotating structure is in a “true” or “actual” initial starting or home position. Typically the pulse count is reset to a value of zero at this point. Whenever a pulse is subsequently received, it is then sensed whether rotation is clockwise or counter-clockwise as shown in decision steps 2, 3, and 4. If clockwise, the pulse counter is conventionally incremented as shown in action step 5. If sensed rotation is counter-clockwise, the pulse counter is conventionally decremented as shown in action step 6.
Each pulse counted corresponds to a predetermined unit change in angular or rotational position of the shaft, as represented by the equation ShaftRotation=KShaftRotationAnglePerPulse×PulsesCounted.
Where an actuator such as a jack includes a gearbox or other mechanical system that translates shaft rotation into linear extension/retraction of a leg portion of the jack, the position, or degree of extension of the jack leg may be precisely calculated by the following equation:
      JackTranslation    =                  K        TranslationPerrotation            ⁢                          ×      ShaftRotation                                    JackPosition          =                    ⁢                      InitialStartingPosition            ⁢                                                  +            JackTranslation                                                        =                    ⁢                      InitialStartingPosition            ⁢                                                  +                                                                  ⁢                      (                                          K                TranslationPerrotation                            ×              ShaftRotation                        )                              
Accordingly, the total number of pulses counted is directly proportional to the distance the jack leg has traveled. The total number of pulses counted represents a position change or translation delta from a jack leg starting position that is unknown to a controller until the controller is “taught” what to consider as being the jack leg starting or “home” position. The homing of an actuator is a task generally performed by an operator before commencing operation of an actuator. Problematically, however, actuator controllers' perception of actual leg position tends to accumulate errors over time due to such factors as mechanical slippage and wear. It's therefore often necessary for an operator to periodically “re-home” an actuator to “remind” the controller as to the actual position of the actuator leg.
It would be desirable for an actuator such as a jack to be able to automatically determine or “learn” what actuator (jack leg) position to consider as being the actuator (jack leg) starting or “home” position so that operator input would not be required, and so that the actuator could occasionally re-home itself after the controller 20 has inevitably accumulated leg position perception errors.